This invention relates to optical communication systems, and more particularly, to a bidirectional optical interleaver.
Demand for voice and data bandwidth in telecommunications networks continues to increase as population grows, work habits evolve (for example, the increased reliance on telecommuting and video/teleconferencing) and business and personal usage of internet-based telecommunications accelerates. Network operators and telecommunications service providers face an increasingly competitive environment that demands low operating and infrastructure costs, and fast supply of new capacity. Operators and service providers are thus motivated to deploy optical telecommunications equipment that maximizes feature and function density within their facilities.
The telecommunications industry has been actively working to develop new technologies to increase network capacity while continuing to meet the financial expectations experienced in today""s less regulated telecommunication landscape. Of particular importance has been the emergence of wavelength division multiplexing (xe2x80x9cWDMxe2x80x9d), which supports the transmission of multiple optical channels (each channel having a different wavelength) on a single fiber. Each channel is modulated with a different information signal to thus provide a substantial increase in data and voice carrying capacity without requiring the installation of new transport media, such as optical cables, in the network.
Dense wavelength division multiplexing (xe2x80x9cDWDMxe2x80x9d) technology is developing as an approach to scale up network capacity even further. In DWDM technology, the optical channels are packed more tightly within the available transmission spectrum. Individual optical channels thus become more closely spaced. Recently, 400 and 200 GHz spacings were common for optical channels. As the state of the art improved, 100 GHz and then 50 GHz channel spacing has become more common. Optical interleaving products have been introduced to address capacity needs by interleaving multiple sets of optical channels into a more densely packed stream. In its simplest form, with 2xc3x971 interleaving, two subsets of optical channels are multiplexed into a single set with half the channel spacing of the subsets. A 1xc3x972 deinterleaver operates in a complementary manner to demultiplex a set of optical channels into two subsets of optical channels where each subset has twice the channel spacing of the input set. The single term xe2x80x9cinterleaverxe2x80x9d is typically used to refer to both multiplexing and demultiplexing functions. Currently, interleavers may be used to support either multiplexing or demultiplexing, but not both functions simultaneously.
Interleavers are utilized in transmission applications include multiplexing (and demultiplexing) in DWDM networks. Optical Add/Drop Multiplexing (xe2x80x9cOADMxe2x80x9d) is another common application. In addition, interleavers may be deployed as an interface among transmission streams having unequal channel spacings to allow existing networks to be gracefully scaled upwards to meet future capacity demands. While current interleaver technology is entirely satisfactory in many applications, some classes of interleavers are physically large while others may be complex to manufacture and thus have high costs. Accordingly, it would be very desirable to reduce size and costs while increasing the feature set and functionalities provided in today""s optical networking infrastructure.
An inventive method and apparatus is provided by a bidirectional optical 1xc3x972 device formed by a cascade of three optical 2xc3x972 devices. The first of two distal end ports of a first 2xc3x972 device in the first tier of the cascade is optically coupled via a first bidirectional optical path to a proximal end port of a second 2xc3x972 device (one of two 2xc3x972 devices in the second tier of the cascade). The second distal end port of the first 2xc3x972 device is optically coupled via a second bidirectional optical path to a proximal end port FL of the third 2xc3x972 device (the other of the two 2xc3x972 devices in the second tier of the cascade).
Each 2xc3x972 device is bidirectional where optical signals propagate through the 2xc3x972 device in the forward and backward directions simultaneously. An input WDM signal is received at a first proximal end port of the first 2xc3x972 device. As the input WDM signal forward propagates through the first 2xc3x972 device (from proximal end to distal end), it is demultiplexed into first and second subsets of optical channels. In some applications of the invention, the channel spacing in each of the first and second subsets may be approximately double that of the input WDM signal.
Third and fourth subsets of optical channels are received, respectively, at a distal end port of the second 2xc3x972 device and a distal end port of the third 2xc3x972 device. As the third and fourth subsets of optical channels backward propagate through the first 2xc3x972 device (from distal end to proximal end), they are multiplexed into an output WDM signal that is output at the second proximal end port of the first 2xc3x972 device. In some applications of the invention, the output WDM signal may have a channel spacing that is approximately half that of the third and fourth subsets. The demultiplexing in the forward direction and multiplexing in the backward direction occur simultaneously to thereby perform bidirectional 1xc3x972 optical demultiplexing and 2xc3x971 optical multiplexing in the 1xc3x972 device.
In illustrative embodiments of the invention, a bidirectional 1xc3x974 demultiplexer, 4xc3x971 multiplexer is disclosed for demultiplexing an input WDM signal propagating in the forward direction into four discrete output channels while simultaneously multiplexing four discrete input channels propagating in the backward direction into an output WDM signal. The bidirectional 1xc3x974 demultiplexer, 4xc3x971 multiplexer is arranged from a two-tiered cascade of three 1xc3x972 devices. The input WDM signal is received at the proximal end of the cascade and the four discrete input channels are received at the distal end. A bidirectional 1xc3x978 demultiplexer, 8xc3x971 multiplexer is also disclosed for demultiplexing an input WDM signal propagating in the forward direction into a eight discrete output channels while simultaneously multiplexing eight discrete input channels propagating in the backward direction into an output WDM signal. The bidirectional 1xc3x978 demultiplexer, 8xc3x971 multiplexer is arranged from a three-tiered cascade of seven 1xc3x972 devices. Optical isolators are disposed at each input of the cascade in both the four and eight channel embodiments (i.e., at the proximal end input for the WDM signal and at each of the distal end inputs for the discrete input channels) to prevent feedback to the signal sources.
In another illustrative embodiment of the invention, an input WDM signal having N channels is received at a first proximal end port of a 1xc3x972 device disposed in a first tier of a cascade of (Nxe2x88x921) 1xc3x972 devices having m tiers where 2m=N. As the input WDM signal forward propagates through the cascade, 1xc3x97N demultiplexing thereby occurs to generate a set of N discrete output channels that are output at respective first distal end ports of the 2xc3x972 devices in the last tier (i.e., the mth tier) of the cascade.
A set of N discrete input channels is received at second distal end ports of the 2xc3x972 devices in the mth tier of the cascade. As the set of N input channels backward propagates through the cascaded array, Nxc3x971 optical multiplexing thereby occurs to generate an output WDM signal that is output at a second proximal end port of the 1xc3x972 optical device in the 1st tier of the cascade. Optical isolators are disposed at the inputs of the cascade (i.e., at the proximal end input for the WDM signal and at each of the N distal end inputs) to prevent feedback to the signal sources.
Advantageously, the invention provides simultaneous multiplexing and demultiplexing through a single optical cascade. By functioning bidirectionally, the invention doubles the feature set while maintaining the same footprint as single function A equipment. In addition, the doubled functionality does not come at twice the cost of single function equipment as only incremental costs are incurred to implement the invention.